Dehydration-hydrogenation of glycerol into 1,2-propanediol at ambient hydrogen pressure

The vapor-phase reaction of glycerol was performed over copper metal catalysts at ambient hydrogen pressure. Glycerol was converted into 1,2-propanediol (1,2-PDO) through the dehydration into hydroxyacetone, followed by the hydrogenation into 1,2-PDO. The yield of 1,2-PDO was limited up to 80% at a constant temperature of 190 degrees C because of a trade-off problem between the dehydration and the hydrogenation. The dehydration needs relatively high reaction temperatures, whereas the hydrogenation favors low temperatures and high hydrogen concentration. We developed an efficient process during which glycerol was converted into 1,2-PDO with yield higher than 96% in hydrogen flow at gradient temperatures; the dehydration into hydroxyacetone was catalyzed at ca. 200 degrees C, and the following hydrogenation into 1,2-PDO was completed at ca. 120 degrees C. The developed process controls the thermodynamic equilibrium of the second-step hydrogenation. (C) 2009 Elsevier B.V. All rights reserved.